The goal of our research is to determine the mechanism by which the phosphate diester cyclic AMP activates a protein kinase from bovine brain which we have succeeded in isolating and purifying. Although histone phosphatase an cyclic AMP phosphodiesterase activities are absent from our preparation, ATPase activity is seen and is believed to be intimately associated with the protein kinase action, particularly in view of the observed dependence of Pi production on the presence of cyclic AMP. A hypothesis, based on model studies for the binding of cyclic AMP to enzymes which we plan to test, is that this six-membered cyclic phosphate diester acts as a reversible adenylylating agent. If this hypothesis provies to be correct in the case of bovine brain protein kinase, we shall carry out experiments to identify the amino acid to which the phosphoryl group of cyclic AMP becomes attached in the adenylylation process, as well as any residues which assist the formation of the cyclic AMP-enzyme complex. Our findings with a protein kinase cannot fail to have significant implications for the understanding of the multitude of effects which cyclic AMP exhibits in biological systems. BIBLIOGRAPHIC REFERENCES: "The Phosphorylation of Histone Catalyzed by a Bovine Brain Protein Kinase. A Protein Kinase Assay Employing PEI-Cellulose Thin-Layer Sheets", G.W. Moll, Jr. and E. T. Kaiser, J. Biol. Chem., in press (should appear in June or July, 1976).